Wierd output instead of 0s and 1s

A practice excercise from K&R. Kindly read the comments within the
program. I'd be very grateful to people who helped. Why is it that I
get the wierd face-like characters on the screen instead of the
boolean output 0s or 1s?

#include <stdio.h>

/*This program is made to check that leaving the brackets around the
epxression (c=getchar()) in
the statement while ((c=getchar()) !=EOF) produces a boolean output in
C which would either be
0 (false) or 1 (true). This would happen because the relational
operator != has precedence over the assignment
operator =.
*/

void main()
{

int c;

while (c=getchar() != EOF) putchar(c);

/* Surprisingly, it doesn't produce zeros while I type; rather it
produces some wierd characters that look
half like zeros and half like smileys. And doing a Ctrl+Z, which I
thought was the substitute for EOF does
not produce a 1 (true value) */

}

Sathyaish

Sathyaish <> scribbled the following:
> A practice excercise from K&R. Kindly read the comments within the
> program. I'd be very grateful to people who helped. Why is it that I
> get the wierd face-like characters on the screen instead of the
> boolean output 0s or 1s?

Because 0 and 1 are not the same thing as '0' and '1'. Your program
is printing the characters whose character code is 0 and 1, not the
characters '0' and '1' themselves.

> #include <stdio.h>

> /*This program is made to check that leaving the brackets around the
> epxression (c=getchar()) in
> the statement while ((c=getchar()) !=EOF) produces a boolean output in
> C which would either be
> 0 (false) or 1 (true). This would happen because the relational
> operator != has precedence over the assignment
> operator =.
> */

> void main()

Non-standard form of main(). Better would be int main(void).

> {

> int c;

> while (c=getchar() != EOF) putchar(c);

> /* Surprisingly, it doesn't produce zeros while I type; rather it
> produces some wierd characters that look
> half like zeros and half like smileys. And doing a Ctrl+Z, which I
> thought was the substitute for EOF does
> not produce a 1 (true value) */

Note that if c==EOF, the putchar(c) is never called, so your program
will never print a 1 (true value) for any input.

> }

--
/-- Joona Palaste () ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"War! Huh! Good God, y'all! What is it good for? We asked Mayor Quimby."
- Kent Brockman

Joona I Palaste <> scribbled the following:
> Sathyaish <> scribbled the following:
>> #include <stdio.h>

>> /*This program is made to check that leaving the brackets around the
>> epxression (c=getchar()) in
>> the statement while ((c=getchar()) !=EOF) produces a boolean output in
>> C which would either be
>> 0 (false) or 1 (true). This would happen because the relational
>> operator != has precedence over the assignment
>> operator =.
>> */

>> void main()

> Non-standard form of main(). Better would be int main(void).

>> {

>> int c;

>> while (c=getchar() != EOF) putchar(c);

This loop is printing the character whose code is 1 (true value)
as long as getchar()!=EOF. Note that 1 and '1' are not the same thing.

>> /* Surprisingly, it doesn't produce zeros while I type; rather it
>> produces some wierd characters that look
>> half like zeros and half like smileys. And doing a Ctrl+Z, which I
>> thought was the substitute for EOF does
>> not produce a 1 (true value) */

> Note that if c==EOF, the putchar(c) is never called, so your program
> will never print a 1 (true value) for any input.

>> }

I meant, of course, "if getchar()==EOF and therefore c==0, the
putchar(c) is never called, so your program will never print a 0 (false
value) for any input."

--
/-- Joona Palaste () ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Outside of a dog, a book is a man's best friend. Inside a dog, it's too dark
to read anyway."
- Groucho Marx

(Sathyaish) writes:

[rearranging for context]
> #include <stdio.h>
> void main() {
> int c;
> while (c=getchar() != EOF) putchar(c);

> Why is it that I get the wierd face-like characters on the screen
> instead of the boolean output 0s or 1s?

short:
Probably because '0' != 0 and '1' != 1, but maybe because 'void
main()' invokes undefined behaviour.


longer:
You call putchar() with the result of the comparison, which is indeed
0 or 1. On your platform (and the IBM PC BIOS uses this mapping),
characters 0 and 1 are smiley faces. If instead you use
putchar('0'+c)
you should see some of the results you expect.

Note that 'void main()' is not correct. Main must return int, or
anything at all is allowed to happen - the fact that things seem to
behave fairly normally is only one possible interpretation of
'anything at all'.


mlp

Thank you so very much, Joona Palaste. Yeah, I realize I flipped the
zeros and ones in writing the original post.

You're de man!

Kind Regards,
Sathyaish Chakravarthy.



Joona I Palaste <> wrote in message news:<c1v44d$8og$>...
> Joona I Palaste <> scribbled the following:
> > Sathyaish <> scribbled the following:
> >> #include <stdio.h>
>
> >> /*This program is made to check that leaving the brackets around the
> >> epxression (c=getchar()) in
> >> the statement while ((c=getchar()) !=EOF) produces a boolean output in
> >> C which would either be
> >> 0 (false) or 1 (true). This would happen because the relational
> >> operator != has precedence over the assignment
> >> operator =.
> >> */
>
> >> void main()
>
> > Non-standard form of main(). Better would be int main(void).
>
> >> {
>
> >> int c;
>
> >> while (c=getchar() != EOF) putchar(c);
>
> This loop is printing the character whose code is 1 (true value)
> as long as getchar()!=EOF. Note that 1 and '1' are not the same thing.
>
> >> /* Surprisingly, it doesn't produce zeros while I type; rather it
> >> produces some wierd characters that look
> >> half like zeros and half like smileys. And doing a Ctrl+Z, which I
> >> thought was the substitute for EOF does
> >> not produce a 1 (true value) */
>
> > Note that if c==EOF, the putchar(c) is never called, so your program
> > will never print a 1 (true value) for any input.
>
> >> }
>
> I meant, of course, "if getchar()==EOF and therefore c==0, the
> putchar(c) is never called, so your program will never print a 0 (false
> value) for any input."